Before disassembling, first measure the temperature of the LED bulb in the lighted state (Figure 2, Figure 3). The purpose is to confirm whether the difference in the base (heat dissipation) that is significantly different in appearance is reflected in the temperature. The light from the LEDs contains very little infrared light, so the part of the lamp that is illuminated by the light is not too hot. However, the base is the heat sink of the LED chip , so the temperature is high. At this time, a tape having an emissivity of 0.95 was attached to a portion where the base was the hottest (near the mounting position of the LED), and the temperature of the tape was measured by a thermal imager. 
Among the 9 LED bulbs, the highest surface temperature of the base is the 7.2W product of Toshiba Lighting Technology (Fig. 2(b)). Comparing in Group A, Samsung LED's 7.1W product is about 47°C, Qinshang Optoelectronic's 7.5W product is about 43°C, and Toshiba Lighting's 7.2W product is about 61°C, which is higher than these two models. 14 to 18 ° C.
Figure 2: Temperature measurement of LED bulbs in Group A
Note: A tape with an emissivity of 0.95 was attached to the base of the LED bulb, and the temperature of the tape was measured using a thermal imager "TH6300" from NEC Avio Infrared Technology. A tape having an emissivity of 0.95 was used in order to unify the emissivity at the measurement position to 0.95. By measuring the temperature on the tape, an accurate temperature can be obtained. The closer the emissivity is to 1, the better the heat sink will be. In addition, the temperature measurement was assisted by the representative of the Thermal Design Laboratory, Guo Feng Shangshu. The measurement performed after lighting the LED bulb for more than 10 minutes. Toshiba Lighting's 7.2W product has a lower emissivity due to its lower emissivity, but the actual surface temperature is lower, but it is actually as high as 61 °C.
Figure 3: Surface temperature of group B (click image to enlarge)
Note: Taiwan's Star Comgistic Capital's 4W product uses a large base that does not match the power consumption. The surface temperature is 38 ° C, the lowest among the 9 products.
The calculation of the emissivity of the base shows that the 7.2W product of Toshiba Lighting Technology is about 0.37, the 7.1W product of Samsung LED is about 0.6, and the 7.5W product of Qinshang Optoelectronics is about 0.64. A low emissivity means that a material that does not easily dissipate heat from the base to the outside is used. The bases of Samsung LED and Qinshang Optoelectronics are made of aluminum die-casting parts with heat sinks, while the base of Toshiba lighting technology is made of thin aluminum plates. Although Toshiba Lighting stated that “the rate of emissivity is improved by the alumite treatment of the surfaceâ€, this value is still lower than other companies in our measurements.
Even if the surface temperature of the base reaches about 61 °C, "there is no problem in actual use" (Toshiba Lighting Technology). The base temperature of the LED bulb is determined by each manufacturer according to the independent standard. "Even if the surface temperature is slightly higher, if the bonding temperature of the LED chip can be kept below a certain value, the luminous efficiency and life, etc. will not be affected" (the technician of the LED bulb manufacturer). Conversely, “it is important in terms of design to allow the surface temperature to rise as much as possible to minimize the heat dissipation mechanism†(the technician). That is to say, in terms of thermal design, the performance indicators of overseas manufacturers still have a little room.
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